In recent years, a communication system using RFID technology has been widely used. In this communication system, a reading/writing device (hereinafter, simply referred to as a tag reader) and an RF (Radio Frequency) tag perform radio communication. The RF tag includes a small IC (Integrated Circuit) chip. The IC chip stores individual identification information and a predetermined arithmetic processing function, thereby enabling management of each individual attached with an RF tag and management of various data sets associated with the respective individuals. Examples of the communication system using the RF tag include an article management system that manages goods in stock or fixtures and a railway ticket examining system.
Here, a power supply method for the RF tag includes a method for an active RF tag and that for a passive RF tag. The active RF tag is driven by an internal power supply. The passive RF tag is driven by a power supply from a tag reader.
For the power supply to the passive RF tag, the following methods are used. One method is to use an electromagnetic induction effect caused by magnetically coupling one coil antenna on the tag reader side and another coil antenna on the RF tag side. Another method uses a received power of electromagnetic waves from the tag reader. These power supply methods are properly used depending on frequency bands used for communication. For example, the power supply method using the electromagnetic induction is employed by an RF tag that performs communication using frequencies in the High Frequency (HF) band. Meanwhile, the power supply method using the received power of electromagnetic waves is employed by an RF tag that performs communication using frequencies in the Ultra High Frequency (UHF) band.
Incidentally, various methods have been proposed for the communication system using the RFID technology. One method is to attach an RF tag to a mobile communication system (see, e.g., Japanese Laid-open Patent Publication No. 2002-247157). Another method is to make it possible to integrate a plurality of RF tags having different functions (see, e.g., Japanese Laid-open Patent Publication Nos. 2006-048094 and 2006-172040). These methods may realize an advanced communication system. Particularly, a method for integrating two RF tags having different applications to enable data sharing may provide more convenient services (see, e.g., Japanese Laid-open Patent Publication No. 2004-046904).
However, the method described in the Japanese Laid-open Patent Publication No. 2004-046904 gives no consideration to a data sharing method performed when integrating a plurality of passive RF tags each performing communication using electromagnetic waves in different frequency bands (e.g., the HF band and the UHF band). When the frequency bands used by the respective passive RF tags are different such as the HF band and the UHF band, the power supply methods for the respective passive RF tags are different as described above. In short, when using the RF tags in combination, the RF tags are driven by independent power supplies. Therefore, this method has difficulty in providing areas enabling data sharing between the respective RF tags.